1. Field of the Invention
The present invention relates to a duplexer device, and particularly, it relates to a duplexer device using a surface acoustic wave filter.
2. Description of the Related Art
In recent years, in connection with the development of mobile communication systems, a portable phone and a portable information terminal have been quickly spread and have been demanded to have a small size and high performance.
The frequency bands used include various ranges, such as an 800 MHz to 1 GHz band and a 1.5 GHz to 2.0 GHz band.
In the development of portable phones in recent years, terminals are made to have high performance by having dual mode (such as a combination of an analog mode and a digital mode, and a combination of two digital modes, TDMA (time division multiple access) and CDMA (code division multiple access)) and dual band (a combination of a 800 MHz band and a 1.9 GHz band, and a combination of 900 MHz band and a 1.8 GHz band or a 1.5 GHz band).
Under the circumstances, parts used in the portable phone (such as a filter) are also demanded to have high performance. Furthermore, miniaturization and a low production cost are also assumedly demanded in addition to the high performance.
In the mobile communication equipments, an antenna duplexer is used as a component of an RF (radio frequency) part conducting branching and generation of signals transmitted and received by an antenna.
FIG. 20 shows a constitutional block diagram of a radio frequency part of a portable phone that has been conventionally used.
An audio signal 100 input from a microphone is transformed into a modulation signal of the modulation mode of the portable phone system by a modulator 101, and after further transformed into a prescribed carrier frequency by a local oscillator 108, it passes through an inter-stage filter 102 selecting only a signal of the prescribed transmission frequency and amplified to a desired signal intensity by a power amplifier 103 to feed in an antenna duplexer 105. The antenna duplexer 105 feeds only a signal of the prescribed transmission frequency to an antenna 104, which is then transmitted to the air as a radio signal from the antenna 104.
On the other hand, a signal received by the antenna 104 is fed to the antenna duplexer 105, and only a signal of a prescribed frequency is selected. The selected reception signal is amplified by a low noise amplifier 106, and after passing through an inter-stage filter 107, only a message signal is selected by an IF filter and taken out as an audio signal 100 by a demodulator 111. The antenna duplexer 105 is positioned between the antenna 104 and the so-called audio signal processing circuit and distributes the transmission signal and the reception signal to prevent interference of them.
An antenna duplexer requires at least a transmission filter and a reception filter and also has a matching circuit (which is also referred to as a phase matching circuit or a line pattern for phase matching) for preventing interference of the transmission signal and the reception signal.
An antenna duplexer of the high performance terminal includes a duplexer using a dielectric material, a composite duplexer using a surface acoustic wave filter with a dielectric material in at least one filter, and a duplexer using only a surface acoustic wave filter. The duplexer using a dielectric material has a large size, and thus it is difficult to produce a portable terminal equipment of a compact size and a small thickness.
In the case of an antenna duplexer using a surface acoustic wave filter in one filter, it is difficult to achieve a compact size and a small thickness due to the size of the dielectric material device.
The conventional duplexer device using a surface acoustic wave filter includes a modular type having a filter and a matching circuit separately carried on a printed circuit board and a one-piece type having transmission, and reception filter chips in a multi-layer ceramic package and a matching circuit inside the duplexer package.
The duplexer device of this type has a compact size and a small thickness, i.e., from ⅓to {fraction (1/15)} in volume and from xc2xd to ⅓ in height of the conventional duplexer using a dielectric material. It is possible to realize the equivalent cost to the dielectric material device by using the surface acoustic wave device and by reducing the device size.
A further demand is expected to reduce the size of the duplexer, and it is necessary therefor to use a structure using a multi-layer ceramic package disclosed in Japanese Unexamined Publication No. Hei 10(1998)-126213, to provide two filters on one chip to apply a flip chip mounting technique using no wire connection. In either case, a xe2x80x9cduplexer packagexe2x80x9d is capable of airtightly sealing two surface accostic wave filters and a xe2x80x9cmatching circuitxe2x80x9d to constitute a duplexer with the two filters.
That is, in order to realize a duplexer device of a compact size and a low cost, it is demand ed to mass-produce duplexer packages having stable characteristics. In order to mass-produce duplexer packages, such a process has been used that package devices are arranged on a ceramic multi-layer sheet in a matrix form, which is divided into respective chips in the final stage after baking. The process is recently improved so that, instead of a sheet (shown in FIG. 4) having the waste part among the respective devices, it is used a sheet of a fine matrix arrangement (shown in FIG. 5) having devices directly arranged, whereby the number of produced devices is improved. In FIGS. 4 and 5, the respective squares indicate duplexer devices. The multi-layer sheet is formed by stacking, for example, five ceramic sheets. The duplexer package is produced mainly by the stacking step and the baking step subsequently conducted.
What is brought question is accuracy influenced by deviation of layer accumulation caused upon making a multi-layer structure of plural ceramic sheets.
FIG. 6 shows a cross sectional structure of a conventional duplexer.
The conventional duplexer shown in FIG. 6 has a five-layer structure of from a layer 1 (L1) to a layer 5 (L5), and a lid 5 is arranged on the layer 1 (L1) as the uppermost layer. Filter chips 2 and 3 are mounted on a surface of the layer 4 (L4), and connection terminals on the filter chip and bonding terminals on the layer (L2) are connected with wires 4.
Connection terminals to an outside circuit are arranged on a back surface of the layer 5 (L5).
A line pattern 1 of a phase matching circuit is formed on a surface of the layer 3 (L3) as an internal layer. Furthermore, a side castellation 6 as a connection path to the connection terminal of the layer 5 (L5) is formed from the layer 2 (L2) having the bonding terminals to the back surface of the layer 5 (L5) as the lowermost layer.
Along with reduction in size of a duplexer package, the thickness in the width direction on the side surface of the package is also decreased, and thus such a problem (short circuit problem) occurs in that a pattern formed in the internal layer (for example, the line pattern 1 for phase matching) is in contact with a pattern of the connection part 6 (side castellation) formed on the side surface of the package caused by deviation upon stack of the layers.
When the number of layers, on which the side castellation 6 is formed, is decreased to prevent the contact, the positional accuracy becomes more severe. In the case where the line pattern for phase matching is formed over the plural layers to overlap the upper and lower line patterns, other problems occur in that the characteristics are different from the designed value, and stable characteristics cannot be obtained.
FIGS. 11 to 13 are diagrams for showing simulation results of the phase rotational amount of the line pattern of the conventional phase matching circuit.
FIG. 11 shows the case where a line pattern a is formed in one layer, which has such a structure that the line pattern a is sandwiched by GND patterns (b and c) formed in the upper layer and the lower layer.
Herein, a distance L1 is 0.5 mm, L2 is 0.6 mm, a dielectric constant ∈r is 9.5, a line width W1 of the line pattern is 0.1 mm, and a line length L0 thereof is 24 mm.
FIG. 12 shows the case where one matching circuit is formed as dividing as line patterns a1 and a2 in separate two layers, which has such a structure that the line patterns a1 and a2 are arranged at positions overlapping each other in the vertical direction, i.e., the overlapping direction of the layers, and are sandwiched by GND patterns b and c.
Herein, a distance L3 is 0.5 mm, L4 is 0.3 mm, and L5 is 0.3 mm, and the line width W1 and the line length L0 are the same as in FIG. 11.
FIG. 13 shows the case where one matching circuit is formed as dividing as line patterns a1, a2 and a3 in separate three layers, which has such a structure that the line patterns a1, a2 and a3 are arranged at positions overlapping each other in the direction perpendicular to the paper surface, and are sandwiched by GND patterns b and c. Herein, a distance L6 is 0.3 mm, L7 is 0.2 mm, L8 is 0.3 mm, and L9 is 0.3 mm, and the line width W1 and the line length L0 are the same as in FIG. 11.
It is understood that the phase rotational amount is about 188xc2x0 in the pattern formed in one layer, whereas the rotational amount is decreased to 132xc2x0 and 105xc2x0 when the patterns of the same length are formed by folding as two or three layers as shown in FIGS. 12 and 13. The decrease in rotational amount means deterioration of the matching property among the frequency characteristics of the filter.
Because an antenna duplexer device is used in frequency bands of several hundreds MHz to several GHz, desired frequency characteristics are realized by providing a large number of connection terminals as possible on the duplexer package, and therefore the connection terminals are often formed on peripheries of all the edges of the package. That is, slight deviation in layer accumulation of the multi-layer sheet causes a short circuit problem.
When the patterns form a short circuit, the circuit of the duplexer cannot be constituted, and the desired filter characteristics of the duplexer device cannot be obtained to produce a defective product. Furthermore, in the case where the line patterns of the matching circuit overlap in the upper and lower layers as in FIG. 12, a capacitive coupling is formed between the line patterns a1 and a2, whereby even though the line length is the same, the rotational amount is decreased from the desired designed phase rotational amount, or a leakage signal is formed in the characteristics of the signal terminals. As a result, the frequency characteristics of the two filters constituting the duplexer are deteriorated.
The invention relates to a duplexer device comprising two surface acoustic wave filters having different band center frequencies and a phase matching circuit for matching phases of the two surface acoustic wave filters, wherein the phase matching circuit is composed of one or more line patterns, and at least one of the line patterns is formed as divided among a plurality of internal layers of a multi-layer package, and at least the line. patterns formed on the internal layers adjacent to each other have pattern shapes different from each other.
According to the constitution, a duplexer device having stable filter characteristics and high performance can be provided with low costs in a smaller size than the conventional one.